Image forming systems which exhibit superhigh contrast photographic characteristics (for example with a gamma value of at least 10) are required for improving the reproduction of continuous tones by means of screen dot images and for improving the reproduction of line images in the graphic arts field.
Conventionally, special developers known as lith developers have been used for this purpose. Lith developers contain only hydroquinones as the developing agent. The sulfite which is used as a preservative is in the form of an adduct with formaldehyde. The free sulfite ion concentration is very low (generally not more than 0.1 mol/liter) so as not to interfere with the infectious development. Consequently, the lith developers are very susceptible to aerial oxidation and they have a major disadvantage in that they cannot be stored for more than 3 days.
The methods in which hydrazine derivatives are used, disclosed, for example, in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857 and 4,243,739 are known as methods by which high contrast photographic characteristics can be obtained using stable developers. Photographic characteristics of high speed and superhigh contrast can be obtained using these methods. The addition of high concentrations of sulfite to the developer can be tolerated and consequently, the stability of the developer against aerial oxidation is greatly improved in comparison to that of a lith developer.
However, the above mentioned image forming systems require developers which have a very high pH value and so the developers are susceptible to aerial oxidation. Denaturation of the fixer is likely to occur as a result of the admixture of the developer with the fixer and there is the further disadvantage that there is a heavy burden of neutralization when scrapping used processing liquids.
Progress has been made in the past with nucleation development accelerators to realize high contrast development with developers of a lower pH. The methods in which secondary and tertiary amino compounds are added to the developer as disclosed in the aforementioned literature references, the methods in which amino compounds such as those disclosed in JP-A-63-511, JP-A-63-604, JP-A-63-1124 and JP-A-63-124045 are added to the light-sensitive layer and the methods in which amino compounds such as those disclosed in JP-A-2-170155 are added to the light-sensitive layer, are already known (The term "JP-A" as used herein signifies an "unexamined published Japanese patent application".) However, none of these methods provides a truly satisfactory high contrast, and often they must be used in large quantities. Therefore, the development of a more effective accelerator is clearly desirable.